1. Field of the Invention
This invention is directed generally to a method and apparatus for recovering products such as oils and other chemical residues from tanks or containers used to transport or store such products and particularly to a method and apparatus which provides for the continuous recycling of various solvents or fluids which are used to clean or flush the tanks or containers by separating and purifying the solvents and residual products from a mixture of the same which is passed through a tube and flat plate heat exchanger wherein the solvents are evaporated in a substantially continuous process.
2. History of the Prior Art
It is the general practice in the cleaning of tanks and containers used for the storage and transportation of chemical products including oils, resins, epoxys, paints, and waste chemicals to use water or steam, together with the possible addition of a suitable wetting agent, to spray and flush the interior walls of the container or tank and thereafter collect the mixture of residual product and cleaning fluid. This practice results in a large volume of contaminated waste which must be suitably disposed of in such a manner as to insure no adverse effect upon the ecology. The disposal of contaminated waste has become increasingly more undesirable not only because of increased disposal costs, but because the products being cleaned from the tanks or containers as well as the cleaning solvents are themselves valuable commodities.
In addition to the foregoing, when water is used to clean a tank or container, it is the mechanical action of the fluid impacting against the walls of the tank or container which functions to drive the remaining products from the walls of such tanks and containers. Thus, a large amount of water must be used in a continuous stream to physically separate or force the product from the tank. The larger the quantity of cleaning fluids, the greater the waste disposal problem. By way of example, it takes approximately seven gallons of fluid to wet the walls of a 5,000 gallon tank, however, it may take 400 or more gallons of water to flush a product from the tank walls (with the exact amount depending, of course, upon the type of product being removed, the use of wetting agents, or the addition of heat in the form of steam).
It has been determined that the cleaning of transportation and storage tanks and containers may be more easily and thoroughly accomplished utilizing chemical solvents. These solvents make the residual products within the tanks or containers more soluble and thus have the beneficial effect of reducing the amount of effluent waste which must be handled or disposed of.
The problems which have been encountered with the use of solvent cleaning systems involve the costs and expenses incurred in using the solvents. Once the solvent has been contaminated during a cleaning cycle, it is of no value for further cleaning operations as it now carries a portion of a contaminant with it. Thus, either additional solvent must be used, which increases costs for cleaning fluid supplies, or the used solvent must be purified and collected for reuse. Collecting the solvent presents additional problems in that the type of solvent and its ability to be reclaimed will vary from one solvent to another. It would be preferred to have a cleaning system which is capable of cleaning as many types of chemical products from a tank as is possible, and thus the use of diverse types of solvents would be likely.
Generally, various batch type distillation devices are being used to separate solvents from other products. These batch vaporizors, however, are not totally efficient and do not provide for a continuous flow of contaminated waste or liquid therethrough. In addition, other types of continuous flat plate heat exchangers have been used to separate solvent from other liquids again, however, it is not believed that such distillation equipment permits sufficient utility to provide for the continuous vaporization of a plurality of fluids from a residual product so as to permit each of the fluids to be substantially purified and collected for reuse.